Water pumps for circulating coolant within an internal combustion engine typically employ a shaft mounted and driven impeller to pressurize and move the coolant. The impeller shaft may be gear driven internally of the engine block or driven through an accessory drive system operating outside of the crankcase. In either case it is necessary to provide an adequate seal between the wet, impeller side of the pump and the dry, shaft bearing side. Significant failure of the seal may lead to shaft bearing failure while minor failure erodes operator confidence in the reliability of the seal. Current water pump seal design makes use of a carbon wear disc which is torsionally driven against a stationary bushing portion of the pump housing. As the disc is rotated it establishes a hydrodynamic seal at its interface with the pump housing thereby providing an effective seal. Over the life of the water pump seal, the wear disc is subject to a reduction in thickness due to continued rotation and wear against the pump housing. Effective sealing force is typically maintained between the carbon wear disc and the housing through a spring member which is operable to impart a force on the disc in the direction of the stationary pump housing as well as to torsionally drive the wear disk through a coupling with the impeller. Because the spring has to torsionally drive the wear disc, it has a tendency towards torque wrap-up requiring that it have a higher spring rate than required to maintain the wear disc in contact with the bushing surface. The increased spring rate accelerates the rate of wear on the disc and, consequently, the service life of the carbon wear disc may be reduced.
An elastomeric shaft seal may be used to seal the back side of the carbon wear disc against the waterpump shaft. As the carbon wear disc undergoes its inherent reduction in thickness with service time, the shaft seal slides progressively over the water pump shaft to remain in contact with the back of the wear disc and thereby maintain a coolant-tight seal. Because of the long wear process, the seal is prone to damage due to debris which could become lodged between the surface of the shaft and the seal. Such seal damage may lessen the useful life of the seal.